1. Field of the Invention
The invention relates to digital image enhancement process and more particularly to a process for enhancing digital video.
2. Description of Related Art
The most common image enhancement techniques include histogram equalization, dynamic range stretching, gamma adjustment, logarithmic enhancement, as well as others. Histogram equalization is a process of adjusting the image so that each intensity level contains an equal number of pixels. In many cases, this can improve the appearance of the image by balancing light and dark areas. Other times, it degrades the image's appearance by accentuating image defects. This is particularly true with JPEGs.
Gamma adjustment is a method of tonal correction that takes the human eye's perception of neighboring values into account. Gamma adjustment balances the shadows and highlights in an image by keeping black as black and white as white, but making a non linear transition between the two. Gamma can be used to make shadows less deep, or highlights less washed out.
Logarithmic enhancement relies on a logarithmic scale to enhance images rather than a linear scale because the human eye has a logarithmic intensity response while some images are digitized by equipment that quantizes the samples on a linear scale. To make the image better for use by a human observer, these images may be made to have a logarithmic response.
Previous patents in this field include U.S. Pat. No. 6,580,835 to Gallagher which improves digital images by performing a normalized tone scale conversion based on a central pixel of the image.
U.S. Pat. No. 5,991,456 to Rahman et al. describes a method for improving a digital image which calculates the image intensity at specified positions and adjusts the image intensity according to a mathematical equation. The process described in the Rahman patent is also know as “Multi-Scale Retinex.”
U.S. Pat. No. 5,640,469 to Lewins et al. describes a method for improving images obtained from infrared or x-ray systems which do not obtain the image using visible light. The method improves the intensity equalization of the obtained image data.
An object of the present invention is to provide a method for enhancing digital images.
Another object of the present invention is to provide a method for enhancing digital images captured in dark, foggy or underwater environments.
Another object of the present invention is to provide a method for enhancing digital images which enhances the luminance and color in separate steps.
Another object of the present invention is to provide a method for enhancing digital images which enhances the luminance of the image by increasing the brightness of dark portions of the image more significantly than the bright areas of the image.
Yet another object of the present invention is to provide a method for enhancing digital images which is capable of enhancing digital video streams in real time.
Finally, it is an object of the present invention to accomplish the foregoing objectives in a simple and cost effective manner.